1. Field of the Invention
The invention relates to the field of liquid flow. More particularly, the invention relates to a method and device for sensing the presence of a flowing liquid. By way of further characterization, but not by way of limitation thereto, the invention senses the presence of a flowing liquid by monitoring the resistance change in a thermistor located in the path of the flowing liquid.
2. Description of the Related Art
In high speed mechanical apparatus such as centrifuges, it is extremely important that the rotating parts be lubricated both for friction and cooling purposes. That is, in a device such as a high speed centrifuge, oil flow around the rotor shaft and other moving parts of the centrifuge is critical in that a failure of oil flow in these parts could cause a mechanical failure in the device. Such a failure could result in destruction of the device.
Prior centrifuge devices have employed sensors to detect the voltage supplied to the oil pump motor. That is, these devices sense whether the oil pump receives power. However, these devices could not sense whether there was a mechanical breakdown in the oil pump, a stalled pump, or a leak in an oil line resulting in a loss of oil flow to the shaft.
Thermistors and Wheatstone bridges have been employed previously to monitor liquid temperatures. For example, devices such as that disclosed in U.S. Pat. No. 3,918,636 issued to Walter F. Dawson on Nov. 11, 1975 have employed thermistors and Wheatstone bridges to monitor water temperature. However, these devices have not been used to monitor oil flow in an apparatus where oil flow is critical to the operaton of the device and the safety of observers or technicians working in the area.